long reads

A GLIMPSE of a mosquito circling me or hearing the buzz of its wings as it passes my ear always puts me on edge, especially during the day. I know how debilitating and even deadly the dengue fever virus can be, and I know that the mosquitoes that spread it normally only bite in the daytime.

In contrast to mosquitoes that strike after sundown, the bite from these mosquitoes usually goes unnoticed, but it can be infinitely more perilous.

Vectors – the organisms that carry a pathogen and are able to pass it on to a new host – for dengue are two species of mosquitoes in the genus Aedes aegypti and, to a lesser extent, female Aedes albopictus. They are responsible for the relentless spread of dengue in Thailand and more than 100 other countries around the world. The World Health Organization (WHO) warns that the epidemiology of dengue is rapidly evolving as outbreaks occur with increasing frequency and are expanding to previously unaffected geographical areas. Dengue flourishes in impoverished urban and rural areas but also takes a toll in more affluent neighbourhoods in tropical and subtropical countries.

Various species of Aedes mosquitoes also carry the viruses that cause diseases such as chikungunya, dog heartworm, eastern equine encephalitis, yellow fever and West Nile encephalitis. Of all insects on Earth, mosquitoes are the perfect vectors for spreading deadly viruses because of their ability to rapidly place them in the blood of large numbers of people and animals.

Aedes aegypti is most active approximately two hours after sunrise and several hours before sunset. This mosquito prefers to bite indoors and usually avoids detection because it approaches from behind and bites on the ankles and elbows. Aedes aegypti mosquitoes are also the prime vectors of the Zika virus that is causing worldwide panic because of the danger it presents to pregnant women and their unborn children. Several cases have been reported in Thailand.

Aedes albopictus is an aggressive daytime biter whose peak feeding times are early morning and late afternoon. This mosquito lands and bites quickly and is usually off again before the victim has time to swat it. It bites outdoors or indoors, but is usually found outside. Albopictus is strongly attracted to humans but also feeds on cats, dogs, birds and other animals.

Some victims ‘lucky’, others lose everything

Having written several stories on dengue fever in Thailand, I am quite familiar with official statistics that reveal an alarming upswing in cases in recent years. But I’m also acquainted with dengue in a more personal way. Three friends of mine contracted dengue fever in 2015. Two live in houses in different parts of Bangkok and the third, a middle-aged lady Miss Bangon, rents an apartment off Sukhumvit Road in Samut Prakan province. She was willing to go on record to describe her experience with dengue.

“In the beginning of September I experienced flu-like symptoms, including high fever, headache and loss of appetite. I went to see a doctor after three days. He did a blood test and based on the results he diagnosed me with dengue fever. I was immediately admitted to a hospital where I underwent treatment. I was discharged after two days feeling much better and I fully recovered a few days later. Officers from the local administration office came to fumigate my room, the apartment complex and the surrounding area,” said Miss Bangon.

The experiences of my other two friends were quite similar. They can all be considered lucky, because even though they became very ill they survived and apparently aren’t suffering any lingering effects of the virus. But for many others in Thailand last year, a brush with dengue resulted in death. This includes 37-year-old popular TV actor Thrisadee “Por” Sahawong.

Much of the nation followed his heartbreaking and ultimately fatal struggle with the mosquito-borne virus. Por was admitted to Ramathibodi Hospital on November 9 and underwent several operations, including amputation of his infected left foot above the ankle on November 20. He was in a coma for more than two months before he was pronounced dead on January 18 after developing a severe infection in his right lung.

The whole nation grieved at the news of Por’s death. The handsome actor was an ambassador for the World Society for the Protection of Animals and was involved in other charitable projects to benefit groups such as poor farmers. He left behind his wife, Vanda, and two-year-old daughter, Mali. The only consolation is that his illness was covered extensively in the media and put a much-needed spotlight on a disease that claimed a record number of victims in Thailand in 2015.

Thailand under siege

Just one day after Por’s death the Ministry of Public Health (MOPH) announced that 142,952 people were infected with dengue in Thailand in 2015 and 141 succumbed to the disease. Dr Sopon Mekhton, Permanent Secretary of the MOPH, warned that the number of infections in 2016 could rise to 166,000, a 16 percent increase. Dr Sopon also disclosed that the number of dengue fever cases diagnosed from January 1-20 in Thailand’s 67 provinces was 2,380, with most patients between the ages of 15 and 24. No deaths were reported for this time period. The highest levels of dengue transmission occur during the rainy season which usually starts in May or June.

According to the MOPH, dengue ranks second in the list of diseases posing the greatest risk to Thais, after pneumonia. One doctor who asked not to be identified expressed frustration that “even though medical professionals in Thailand have been fighting the dengue virus for more than 50 years, and it should be possible to control the risk of transmission, we have to accept that infection is still very common and presents a growing problem in the country.

“Once cured, the patient is protected for life against dengue, but only against the particular strain he was stricken with. There are four disease-causing strains,” explained the doctor, adding that the mortality rate for dengue is actually rather low compared to cancer or even car accidents. He also pointed out that there are more than 3,500 known species of mosquitoes and only a small fraction of them are disease vectors.

Global threat

Thailand is not the only country in Southeast Asia that was ravaged by dengue fever in 2015. Singapore, Malaysia, Vietnam and the Philippines were also badly hit, as were countries in different parts of the world, notably Brazil, India and Mexico. Basically, dengue is on the rise worldwide.

The WHO says dengue is now the most common and most rapidly spreading mosquito-borne viral disease affecting humans, and it has become a major international public health concern. A WHO factsheet released in May 2015 cites studies that estimate there are now around 390 million dengue infections per year, of which 96 million can be considered serious, and that 3.9 billion people in 128 countries are at risk of infection. An estimated 500,000 people with severe hemorrhagic dengue fever, a large percentage of them children, require hospitalisation each year. About 2.5 percent of these patients die. The WHO says it is likely that a great many dengue cases go unreported and misclassified.

The dramatic increase in dengue cases in recent decades has created fears of a global pandemic. Before 1970, only nine countries had experienced severe dengue outbreaks, but the incidence of the virus has increased 30-fold over the last 50 years. Dengue is now endemic in Africa, the Americas, the Eastern Mediterranean, Southeast Asia and the Western Pacific. What’s more, the principal vectors of dengue have continued to silently expand their distribution globally and are now present in more than 150 countries. In an unprecedented move, Governor of Hawaii, David Ige, proclaimed on February 12 a state of emergency in a move to fight mosquito-borne diseases such as dengue fever and Zika. The decision was prompted by an outbreak of dengue in which 250 cases had already been reported. As yet there have been no confirmed cases of Zika.

Help on the way?

In the midst of dengue fever’s ever fiercer attack on humankind, there is hope on the horizon. Sanofi Pasteur, the vaccines division of French pharmaceutical company Sanofi, has announced the development of Dengvaxia®, which is apparently effective against all strains of dengue. Thai scientists reportedly took part in the development studies. In a series of statements last December Sanofi Pasteur announced that the vaccine has been approved in Mexico, the Philippines and Brazil. In February, Jarung Muangchana, director of the National Vaccine Institute, said the Thai Food and Drugs Administration is considering registration of the vaccine.

According to the pharmaceutical company, Dengvaxia® is the first vaccine licensed for the prevention of dengue in the world and is the result of two decades of research. The vaccine has undergone 25 clinical trials in 15 countries around the world, in which more than 40,000 volunteers participated. About 29,000 of the volunteers received the vaccine. The company says that when full production capacity is realised it will be able to produce 100 million doses of the vaccine annually.

Dengue at a glance

Dengue fever is a flu-like viral infection transmitted to humans by the bite of an infected female mosquito of the Aedes aegypti and sometimes Aedes albopictus species, which are found throughout the world. There are four distinct but closely related serotypes of the virus that cause dengue: DEN-1, 2, 3 and 4. The incubation time is from 3-14 days, most often 4 - 7 seven days.

The first recorded mention of symptoms compatible with dengue fever was in China during the Jin Dynasty (265-420 AD), when it was called a “water poison” and associated with insects. News of an epidemic in Batavia (present-day Jakarta) of an illness that sounds a great deal like dengue fever was reported in medical literature in 1779. In 1780 US physician Benjamin Rush coined the term “break-bone fever” in reference to the extreme discomfort dengue patients usually feel in their movements due to intense joint and muscle pain. The dengue virus was first isolated in 1943.

During the last part of the 20th century, many tropical regions of the world saw an increase in dengue cases. Thailand recorded its first official cases of dengue in 1949, and the country has experienced five major epidemics since then.

The first dengue hemorrhagic fever (DHF) outbreak was reported in Bangkok in 1958. There were 2,158 cases and 300 deaths. In 1987 a major outbreak caused a reported 174,285 cases of dengue and 1,007 deaths. Two large outbreaks followed back-to-back in 1997 and 1998, with 101,689 cases and 253 deaths, and 126,348 cases and 432 deaths respectively.

The outbreak last year was the second biggest since 1987 with regard to number of cases, but the number of fatalities was relatively low at 141. This must be attributed to advancements in treatment.

Dengue fever has three forms or classifications based on its severity.

Symptoms of typical uncomplicated classic dengue usually start with fever up to 105 degrees Fahrenheit within four or five days after the bite of an infected mosquito, and may also include severe headache (mostly in forehead), pain behind the eyes which worsens with eye movement, severe joint and muscle pains and aches, swollen lymph nodes, nausea, general weakness, vomiting, skin rash, sudden chills, diarrhoea and loss of appetite.

Symptoms of DHF include all of the above plus pronounced damage to blood and lymph vessels, causing bleeding from the nose and gums and purplish bruises. This form of dengue fever can cause death.

The most severe and dangerous form of the disease is dengue shock syndrome (DSS). It includes all of the symptoms of classic dengue and DHF, plus fluids leaking from blood vessels, massive bleeding and shock due to very low blood pressure. DSS generally occurs when an infected person goes to the hospital too late and the disease has already affected vital organs. The prognosis for DSS is not good, but some patients do survive if they receive the appropriate intensive care treatments.

The Aedes aegypti mosquitoes that spread the dengue virus usually live indoors and near humans, their primary food source. The mosquitoes like to rest in cool, shaded places such as laundry areas, under tables and in wardrobes. They feed during daylight hours, often biting people around the feet and ankles. The bite is painless. The dengue virus cannot be transmitted from person-to-person.

People who suspect they may be suffering symptoms of dengue fever should see a doctor at once. There’s no specific medication to kill the virus but there’s no doubt that medical intervention saves lives. For severe dengue symptoms, including shock and coma, early and aggressive emergency treatment with fluids and electrolyte replacement can be life-saving. One treatment involves the intravenous administration of blood platelets.

Most people with uncomplicated dengue recover completely within about two weeks, but others may go through several weeks to months of feeling tired and/or depressed. Some victims say they experience lingering effects many years after infection with the dengue virus. To speed recovery, healthcare experts recommend getting plenty of bed rest, drinking lots of fluids and taking medicine to reduce fever, although some doctors advise against taking aspirin.

The mosquitoes that transmit the dengue virus often breed in used automobile tires, flower pots, old oil drums and other man-made containers like earthenware jars, metal drums, concrete cisterns and discarded plastic containers. The infected mosquitoes may also live and rest indoors, in closets and other dark places. Outside, they rest where it is cool and shaded.

To prevent being bitten, avoid areas with standing water, and wear long-sleeve shirts and long trousers or dresses during the daylight hours when the mosquitoes are most active. Other suggested preventive measures include the use of coils, electric vapour mats, mosquito nets and screens, and mosquito repellant sprays containing DEET.